target-sparc: Use official add2/sub2 interfaces for addx/subx

Signed-off-by: Richard Henderson <rth@twiddle.net>
target-sparc: Use mul*2 for multiply

Signed-off-by: Richard Henderson <rth@twiddle.net>
target-sh4: Use mul*2 for dmul*

Signed-off-by: Richard Henderson <rth@twiddle.net>
target-unicore32: Use mul*2 for do_mult

Signed-off-by: Richard Henderson <rth@twiddle.net>
target-xtensa: Use mul*2 for mul*hi

Signed-off-by: Richard Henderson <rth@twiddle.net>
target-xtensa: Use add2/sub2 for mac

Signed-off-by: Richard Henderson <rth@twiddle.net>